I’ve been familiar with NewSID, so my first suggestion was to run that, however, that has a known problem or two. So we then ran Sysprep. The default with Sysprep is :

Having done that, we discovered that the SIDs were still the same. What we needed to do was tick the “generalize” checkbox. (I’m sure this is a nice explanation of that option somewhere, but for now take look here – first post)